The present invention relates generally to medical devices, and more particularly provides an improved syringe and inflatable catheter apparatus which incorporates a uniquely configured volume and pressure-limited gas syringe used to internally pressurize the catheter portion of the apparatus.
Potential over-pressurization of inflatable catheter elements used to internally block various body passages, such as the pulmonary artery, is a well known and long-standing problem in the practice of medicine. Pulmonary artery catheters are typically provided at their distal end with a small balloon which is selectively inflatable by a gas syringe connected to the catheter's gas-receiving inlet. To utilize the catheter, a sheath element is inserted into a suitable vein, such as the jugular vein, and the distal end of the catheter is fed through the sheath into the vein. When the distal end of the catheter exits the inner end of the sheath, the balloon is inflated. The inflated balloon acts as a "float" to assist in further insertion of the catheter by drawing its distal end through the vein (by virtue of the blood flow therethrough) and ultimately into a position in which the inflated balloon becomes "wedged" in a branch of the pulmonary artery. Lodged in a pulmonary artery branch in this manner the distal end of the catheter may be utilized in a conventional manner to monitor the pulmonary artery "wedge" pressure via the resulting pressure trace pattern on an oscilloscope operatively connected to the catheter.
After this initial wedge pressure reading is taken the balloon is deflated, but the catheter is normally left in place so that the balloon may be re-inflated to take subsequent wedge pressure readings. The over-pressurization problem previously mentioned typically arises when, between these intermittent balloon inflations, the distal catheter end "migrates" into a smaller portion or branch of the pulmonary artery. Subsequent balloon inflation then takes place in an unintended arterial portion which may be weaker and/or of a smaller interior cross-section than anticipated. If great care is not exercised in re-inflating the catheter balloon in these instances, the balloon can be over-pressurized and cause the artery to burst.
Typically, the catheter has a design inlet gas volume capacity corresponding to the gas volume required to fully inflate the balloon. In a variety of conventional manners the syringe is volume-limited to assure that no more than this designed-for gas volume can be forced into the catheter from the syringe to thereby prevent over-inflation of the balloon.
However, even with this volume "matching" between the syringe and catheter it is possible to cause over-pressurization of the catheter balloon during the intermittent reinflation thereof, and concomitant rupture of the artery portion into which it has migrated, if the syringe is not correctly and carefully used by its operator. Specifically, during each subsequent reinflation of the balloon the syringe plunger must be moved slowly toward the end of its stroke within the syringe body to avoid inordinately high "peak" pressures in the inflating balloon. Even the proper slow movement of the syringe plunger can cause the balloon to rupture the smaller or weaker artery portion if the plunger is pushed too far and too hard by the syringe operator.
The operational safety of conventional pulmonary artery catheters (as well as other types of syringe-operated inflatable catheters) is thus to a large degree dependent upon the "feel" transmitted to the syringe plunger as the catheter interior pressure is being increased, and the syringe operator's skill in interpreting and reacting to such "feel". Even though the pressure trace on the catheter-connected oscilloscope will normally indicate when the artery portion has been sufficiently occluded by the inflating balloon (by generating a recognizable "wedge" pattern), certain heart infirmities (such as an incompetent mitral valve) can generate a potentially misleading trace pattern which, even though the partially inflated balloon is fully blocking the artery portion, indicates that further balloon inflation is needed. It is this further balloon inflation which, in conventional volume-limited syringe and catheter apparatus, can easily burst the artery.
Various attempts have been previously made to eliminate this over-pressurization problem. For example, as exemplified in U.S. Pat. Nos. 3,642,005; 3,905,361 and 4,064,882 inflatable external indicator balloons have been placed on non-inserted portions of catheters to provide the syringe operator with an additional visual indication of the degree of inflation reached in the internal catheter balloon. Other supplemental visual internal catheter pressure indicia, such as simple pressure gauges have also been utilized. These and other visually oriented safety devices, however, must (along with the oscilloscope trace pattern) be continually watched by the syringe operator, and properly reacted to, to be effective. Also, particularly in the case of pressure gauges, moving parts are involved which are always subject to malfunction and wear.
Other mechanical devices, such as pressure relief valves, have also been used to actually limit the pressure supplied to the catheter. Illustrative devices of this type may be found in U.S. Pat. Nos. 3,871,374; 4,116,201 and 4,439,185. Other representative syringe and catheter devices may be found in U.S. Pat. Nos. 4,335,723; 4,370,982 and 4,583,974. The problem with mechanical pressure-limiting devices such as multi-component pressure regulators or relief valves is that they are subject, like all devices with moving parts, to malfunction or failure.
It can be seen from the foregoing that a long-standing need exists for improved syringe and inflatable catheter apparatus having greater operational safety from a catheter over-pressurization standpoint. Accordingly, it is an object of the present invention to provide such apparatus.